Tate — List of Irish Liassic Fossils. 23 



posteriorly ; anterior margin rounded, posterior produced, obliquely ? trun- 

 cated (the posterior margin is represented in the figure as complete ; the shell 

 is imperfect in this region). 



An obtuse, ill-defined keel proceeds from the umbo to the lower posterior 

 angle, another to the upper posterior angle, enclosing a broad, deeply-impressed 

 lunular area. Marked by concentric plications and fine striae, and close-set 

 radiating granular lines. Length, 75 inch ; breadth, 1 '5 inch ; thickness, 

 •5 inch. 



Geological Position. — Zone of " A. angulatus," Island Magee, Co. Antrim. 



27. Discina Holdeni, Tate, Quart. Jour. Geol. Soc, Vol. xxiii., p. 314 

 (1867). id. Geol. Mag., Vol. vi., p. 6 (1869). 

 Discina sp., Terquem and Piette. Lias Inf. de l'Est de France ; t. xiv., 

 figs. 33-34, p. 113 (1865). 



Shell small, regularly conical, base orbicular, the length and breadth in 

 the proportion of about 5 to 4 ; summit central ; test concentrically striated ; 

 colour, black to brownish-black ; yellowish-brown in the young shell. Dimen- 

 sions of an averaged sized specimen: — Diameters, 4*5 and 3*6 millimetres; 

 height, 2 '3 millimetres. 



D. Holdeni is distinguished from the other Liassic species of the genus by 

 its regularly conical form and central apex ; and from D. reflexa, Sowerby, 

 with which it has been confounded by the latter character. 



Geological Position. — Ranges from the Zone of "Ammonites angulatus" 

 to that of "Ammonites Ibex," in England, and throughout the Lower Lias in 

 the East of France. 



28. Pollicipes alatus, nov. spec. Plate I. fig. 6. 



The single scutal plate here figured is the one to which Mr. Etheridge 

 (Quart. Jour. Geol. Soc, Vol. xx., p. 114, 1863) applied the M.S. name of P. 

 liassicns ; but, as another species was described by Dunker with a similar 

 denomination, P.liasinus, it appears to me advisable not to adopt Mr. Etheridge's 

 provisional name. I, therefore, have selected that of P. alatus. 



Scutum triangular, flat, apex acute with a lateral wing-like extension upon 

 the oceludent side ; basal margin outwardly curved ; the tergal margin inflated. 

 Exterior surface marked with regular raised lines coincident with the basal 

 margin, and which are prolonged on the wing-like projection, and on the 

 enrolled tergal margin. 



Geological Position. — Zone of " A. angulatus," Island Magee, Co. Antrim. 

 Specimen unique. (P. T. ) 



